Currently, among the models of implementation of patient tables (PTAB) for magnetic resonance systems, particularly for cylindrical magnetic resonance systems, a table board in such a patient table is supported by a body coil (BC) in the magnetic resonance system. The patient table mentioned here comprises various construction components, such as a supporting frame, a table board, a driving mechanism and so on. In which, the body coil is generally a radio frequency body coil fixed on the inner diameter of the magnet. At the same time, gradient coils, including all the gradient coils and shimming coils, are also fixed directly onto the inner diameter of the magnet.
FIG. 1 and FIG. 2 are respective schematic views of two types of patient tables of different models of implementation currently available on the market for use in magnetic resonance systems. As shown in FIG. 1, a gradient coil 102 is fixed directly onto a magnet 101; at the same time, a body coil 103 is also fixed on the magnet 101 via body coil tubes 104 which are in horizontal and vertical directions as shown in FIG. 1. In practical applications, the body coil 103 and its tubes 104 are exhibited as a circular hole, wherein the position of the vertical tube (the tube in the vertical direction shown in FIG. 1) is approximately located at a position that when the circular hole is equally divided into three angles, the position corresponds to the position of two edges of the lower angle of the circular hole; a support frame 105 is fixed at one side of the magnet 101, for example, the right side as shown in FIG. 1; a driving mechanism 106 located on the supporting frame 105 drives a table board 107 to move in the horizontal direction; when it is located outside the magnet 101, the table board 107 is moved on a travel rail (not shown) of the patient table itself, the table board 107, when entering into the magnet 101, is supported by the travel rail of the body coil 103, for example, on a relatively flat region above the body coil 103. The implementation model shown in FIG. 2 is similar to that in FIG. 1, which also comprises construction components such as a magnet 201, a gradient coil 202, a body coil 203, body coil tubes 204, and so on, and what differs from the implementation model shown in FIG. 1 lies only in that a supporting frame 205 in the patient table has no contact with the magnet 201, it is mounted directly on the ground, however, when a table board 207 enters into the magnet 201 under the driving of a driving mechanism 206, the table board 207 is likewise supported by the rail of the body coil 203.
It can be seen that, in both of these two implementation models of the current patient table, they rely on the rail of the body coil to support the table board, thus, in practical applications, they lead to the following problems:
During a scanning process with a magnetic resonance system, the intense current in a gradient coil will cause the gradient coil to vibrate. The reason is that the gradient coil is distorted under the effect of Lorentz force. The distortion is a function of the coil current and is determined by the waveform required by the scanning.
Since the body coil and the gradient coil are both fixed on the magnet, the vibration of the gradient coil will be transmitted to the body coil during the scanning process; therefore, the vibration of the body coil will be transmitted to the table board. This situation generally occurs in the case that the gradient coil operates under an intense load, i.e., the current is continuously large and the intervals between gradient pulses are very short, while the load of the table board is very light, so mechanical resonance vibration occurs. At this time, the vibration frequency of the gradient coil usually covers the natural frequency of the table board, thus it causes the table board to vibrate, and in turn it causes the scanned object carried on the table board, e.g. a human body, to vibrate, particularly when the weight of the object is relatively small, i.e., the load of the table board is relatively small. This situation occurs particularly easily in applications of the pediatric departments, when an infant (with a weight of 2 Kg-20 Kg) is scanned at the scanning position for an adult's brain.
Such vibration would not cause any problem ten years ago and even now in a low field system which only requires a relatively lower image resolution (sizes of pixels are greater than or equal to 2-3 mm). However, with the improvements in the performance of magnetic resonance systems, especially with the ever increasing field intensity and gradient performance, magnetic resonance images of high resolution at a sub-millimeter order have become possible. Under such circumstances, any tiny vibration of amplitude of a sub-millimeter order, for example, the vibration with an amplitude of 0.1 millimeter, will produce serious effects on the image quality, leading to the blurring of image pixels.
Moreover, it has been discovered recently that, the images obtained by high resolution diffusion tensor imaging (DTI) are affected by the serious absence of signals, which may be due to the dephasing caused by vibration. For example, the mechanical vibration caused by the high intensity gradient pulses in the horizontal direction will cause a severe phenomenon of absence of signals. The phenomenon of absent signals actually appears as there is a region at a certain position, for example, a middle position, in an image obtained by scanning which is referred to as a black hole of signals, and DTI analysis cannot be performed on the basis of such image quality; while for the same object and slice position, when more load such as 30 Kg is loaded on the table board, or when the load distribution is adjusted, the phenomenon of absent image signals will be improved significantly due to the reduced vibration.
In summary, in currently available patient tables, since they rely on the rail of the body coil to support the table board, and there also exist mechanical resonances between the body coil and the magnet, the vibration of the gradient coil during scanning will be transmitted from the magnet to the body coil, and eventually causes the vibration of the loaded object on the table board, thus leading to a reduced image quality.